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Posted to user@velocity.apache.org by "Dalrymple, Craig - OCIO-ITS, Kansas City, MO" <Cr...@kcc.usda.gov> on 2012/10/02 00:01:39 UTC

Having trouble doing math with values retrieved from external data source

First, I apologize if this question has come up before, but after doing some lengthy searching, I was unable to find anything related to the issue I am having.

I have included the segment of the template that is causing my headache below. Let me explain a little what I am doing, and give a background on why.

The client I work for has a product from Cisco (Cisco Configuration Engine) for configuring large numbers of network devices. We are trying to make this rather cumbersome tool a bit easier to use. Basically what it does is keep a database of information about each object that can be included into templates, which are then deployed to those objects to keep configurations close to a uniform standard. This tool supports two template formats, the legacy and proprietary .cfgtpl, and .vm which is based on the Velocity Template Engine. Their legacy format allows for some simplification with #include directives and very limited conditional checking --
#if (a == b)
Do this
#else
Do something else
#endif

By limited I mean you can check for equality, and thats all you can check. Oh, and you cannot have nested condition tests. Obviously, Velocity doesn't have this limitation, even on the older version that Cisco has deployed (1.4).

One of the simplifications we would like to include is to handle IP addressing for these network elements. Currently this is input by users, and may or may not be accurate. Since the clients IP addresses conform to a pretty strict standard, the only information we really need is the subnet, and the subnet mask. With this, we can compute the IP addresses.

Below is the segment that has me going even more prematurely bald. I am trying to break an IP4 address into its four parts given the subnet information, then assign the CER IP address (my side of the MPLS connection) by adding 1 to this value, and the PER (carrier side) by adding 2. I have managed to break the address up into a list, and can access the elements directly. However, when I try to manipulate the values it becomes really obvious that I am trying to do addition to strings and not integers.

#set ( $wanSubnet = $!{dsobj.getValue('WAN-Subnet')} ) ## retrieves data from database
! breakupIP($wanSubnet) ## this is a Cisco IOS comment line. It is the only way I can really debug my code, and is included so I can verify that I am getting data.
#breakupIP($wanSubnet) ## macro to break apart the IP address.
! third octet is $addressParts.get(2) ##same as above.
#set ( $octetFour = $addressParts.get(3) ) ## I don't want to change the original value.
! octetFour is $octetFour ## yet another display
#set ( $wanCEIP = $octetFour + 1) ## the math
#set ( $wanPEIP = $octetFour + 2 )
! wanCEIP = $wanCEIP ## display the results.
! wanPEIP = $wanPEIP

The output generated is below. Realize this is part of a much larger template, and I pretty much have to work within the limitations of the tool.

!
! breakupIP(192.168.100.100)
! third octet is 100
! octetFour is 100
! wanCEIP = $wanCEIP
! wanPEIP = $wanPEIP
!

Any help would be appreciated; I am just learning how to do this.

Craig K. Dalrymple
Information Services Consultant (Contractor)
FMI/Unisys Inc. working for
USDA/OCIO/ITS/IOD/NOB
FMI(BPA # AG-3144-B-12-0003)
6501 Beacon Drive
Kansas City, MO 64113
816-926-8819 (W)

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